Film formation method for forming silicon-containing insulating film

ABSTRACT

A silicon-containing insulating film is formed on a target substrate by CVD, in a process field to be selectively supplied with a first process gas including di-iso-propylaminosilane gas and a second process gas including an oxidizing gas or nitriding gas. The film is formed by performing a plurality of times a cycle alternately including first and second steps. The first step performs supply of the first process gas, thereby forming an adsorption layer containing silicon on a surface of the target substrate. The second performs supply of the second process gas, thereby oxidizing or nitriding the adsorption layer on the surface of the target substrate. The second step includes an excitation period of supplying the second process gas to the process field while exciting the second process gas by an exciting mechanism.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a film formation method and apparatusfor forming a silicon-containing insulating film on a target substrate,such as a semiconductor wafer, in a semiconductor process. The term“semiconductor process” used herein includes various kinds of processeswhich are performed to manufacture a semiconductor device or a structurehaving wiring layers, electrodes, and the like to be connected to asemiconductor device, on a target substrate, such as a semiconductorwafer or a glass substrate used for an FPD (Flat Panel Display), e.g.,an LCD (Liquid Crystal Display), by forming semiconductor layers,insulating layers, and conductive layers in predetermined patterns onthe target substrate.

2. Description of the Related Art

In recent years, owing to the demands of increased miniaturization andintegration of semiconductor integrated circuits, it is required toalleviate the thermal history of semiconductor devices in manufacturingsteps, thereby improving the characteristics of the devices. Forvertical processing apparatuses, it is also required to improvesemiconductor processing methods in accordance with the demandsdescribed above. For example, there is a CVD process which performs filmformation while intermittently supplying a source gas and so forth torepeatedly form layers each having an atomic or molecular levelthickness, one by one, or several by several. In general, this filmformation method is called ALD (Atomic Layer Deposition) or MLD(Molecular Layer Deposition), which allows a predetermined process to beperformed without exposing wafers to a very high temperature. Further,the ALD or MLD film formation provides good step coverage, and thus issuitable for filling recess portions of semiconductor devices, such asinter-gate gaps, which have become narrower with increasedminiaturization of the devices. For example, Jpn. Pat. Appln. KOKAIPublication No. 2004-281853 (Patent Document 1) discloses a method forforming a silicon nitride film by ALD at a low temperature of 300 to600° C.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a film formation methodand apparatus for a semiconductor process, which can form asilicon-containing insulating film of high quality at a low temperature.

According to a first aspect of the present invention, there is provideda film formation method for a semiconductor process for forming asilicon-containing insulating film on a target substrate by CVD, in aprocess field configured to be selectively supplied with a first processgas comprising di-iso-propylaminosilane gas and a second process gascomprising an oxidizing gas or nitiriding gas, the method being arrangedto perform a cycle a plurality of times to laminate thin films formed byrespective times, thereby forming the silicon-containing insulating filmwith a predetermined thickness, the cycle alternately comprising: afirst step of performing supply of the first process gas to the processfield while maintaining a shut-off state of supply of the second processgas to the process field, thereby forming an adsorption layer containingsilicon on a surface of the target substrate; and a second step ofperforming supply of the second process gas to the process field whilemaintaining a shut-off state of supply of the first process gas to theprocess field, thereby oxidizing or nitiriding the adsorption layer onthe surface of the target substrate, the second step comprising anexcitation period of supplying the second process gas to the processfield while exciting the second process gas by an exciting mechanism.

According to a second aspect of the present invention, there is provideda film formation apparatus for a semiconductor process for forming asilicon-containing insulating film, the apparatus comprising: a reactionchamber having a process field configured to accommodate a targetsubstrate; a support member configured to support the target substrateinside the process field; a heater configured to heat the targetsubstrate inside the process field; an exhaust system configured toexhaust gas from the process field; a first process gas supply circuitconfigured to supply a first process gas comprisingdi-iso-propylaminosilane gas to the process field; a second process gassupply circuit configured to supply a second process gas comprising anoxidizing gas or nitiriding gas to the process field; an excitingmechanism configured to excite the second process gas to be supplied tothe process field; and a control section configured to control anoperation of the apparatus, wherein, in order to form asilicon-containing insulating film on the target substrate by CVD, thecontrol section is preset to perform a cycle a plurality of times tolaminate thin films formed by respective times, thereby forming thesilicon-containing insulating film with a predetermined thickness, thecycle alternately comprising a first step of performing supply of thefirst process gas to the process field while maintaining a shut-offstate of supply of the second process gas to the process field, therebyforming an adsorption layer containing silicon on a surface of thetarget substrate, and a second step of performing supply of the secondprocess gas to the process field while maintaining a shut-off state ofsupply of the first process gas to the process field, thereby oxidizingor nitriding the adsorption layer on the surface of the targetsubstrate, the second step comprising an excitation period of supplyingthe second process gas to the process field while exciting the secondprocess gas by the exciting mechanism.

According to a third aspect of the present invention, there is provideda computer readable medium containing program instructions for executionon a processor, which is used for a film formation apparatus for asemiconductor process for forming a silicon-containing insulating filmon a target substrate by CVD, in a process field configured to beselectively supplied with a first process gas comprisingdi-iso-propylaminosilane gas and a second process gas comprising anoxidizing gas or nitriding gas, wherein the program instructions, whenexecuted by the processor, control the film formation apparatus toperform a cycle a plurality of times to laminate thin films formed byrespective times, thereby forming the silicon-containing insulating filmwith a predetermined thickness, the cycle alternately comprising: afirst step of performing supply of the first process gas to the processfield while maintaining a shut-off state of supply of the second processgas to the process field, thereby forming an adsorption layer containingsilicon on a surface of the target substrate; and a second step ofperforming supply of the second process gas to the process field whilemaintaining a shut-off state of supply of the first process gas to theprocess field, thereby oxidizing or nitriding the adsorption layer onthe surface of the target substrate, the second step comprising anexcitation period of supplying the second process gas to the processfield while exciting the second process gas by an exciting mechanism.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a sectional view showing a film formation apparatus (verticalplasma CVD apparatus) according to an embodiment of the presentinvention;

FIG. 2 is a sectional plan view showing part of the apparatus shown inFIG. 1;

FIG. 3 is a view showing the structure of the control section of theapparatus shown in FIG. 1;

FIG. 4 is a timing chart showing the recipe of a film formation processaccording to the embodiment of the present invention;

FIG. 5 is a graph showing the relationship of the cycle rate of a filmthickness relative to the set temperature of a process field;

FIG. 6 is a graph showing the relationship of the inter-substrateuniformity of a film thickness relative to the set temperature of aprocess field; and

FIGS. 7A to 7F are views schematically showing a reaction on the surfaceof a Si wafer where di-iso-propylaminosilane gas is used as a siliconsource gas.

DETAILED DESCRIPTION OF THE INVENTION

In the process of developing the present invention, the inventorsstudied problems with regard to conventional methods for forming asilicon oxide film by CVD in a semiconductor process. As a result, theinventors have arrived at the findings given below.

In the case of conventional methods for forming a silicon oxide film,the film formation rate is decreased and/or the film quality of asilicon oxide film is deteriorated with a decrease in the processtemperature, in general. The film formation rate is an important factorthat determines the process throughput, and the film quality of siliconoxide films is increasingly becoming a sensitive issue, along withminiaturization of devices that requires thinner films. For example,where a gate oxide film is formed of a thin silicon oxide film, aleakage current may be increased if the film quality is not good. Underthe circumstances, where a silicon source gas of this kind is used, evenif an ALD or MLD method is employed, the process temperature needs to beset at 300° C. or more, as disclosed in Patent Document 1 describedabove.

However, the temperature used for forming silicon oxide films isrequired to be further lowered. In addition, the quality of formedsilicon oxide films is required to be further improved. Consequently, itis necessary to develop a method for forming a silicon oxide film ofhigher quality at a lower temperature.

In this respect, as a result of studies made by the present inventors,it has been found that, where di-iso-propylaminosilane (DIPAS) gas,which is a univalent aminosilane gas, is used as a silicon source gasalong with an ALD or MLD method, a silicon oxide film of high qualitycan be formed with a predetermined film formation rate being maintainedeven if the process temperature is set at a far lower value than theconventional temperature. In this case, it is possible to furtheralleviate the thermal history of semiconductor devices in manufacturingsteps, thereby improving some of the characteristics of the devices.

An embodiment of the present invention achieved on the basis of thefindings given above will now be described with reference to theaccompanying drawings. In the following description, the constituentelements having substantially the same function and arrangement aredenoted by the same reference numerals, and a repetitive descriptionwill be made only when necessary.

FIG. 1 is a sectional view showing a film formation apparatus (verticalplasma CVD apparatus) according to an embodiment of the presentinvention. FIG. 2 is a sectional plan view showing part of the apparatusshown in FIG. 1. The film formation apparatus 1 has a process fieldconfigured to be selectively supplied with a first process gascomprising DIPAS gas as a silicon source gas, and a second process gascomprising oxygen (O₂) gas as an oxidizing gas. The film formationapparatus 1 is configured to form a silicon oxide film on targetsubstrates by ALD or MLD in the process field.

As shown in FIG. 1, the film formation apparatus 1 includes anessentially cylindrical reaction tube (reaction chamber) 2 arranged suchthat its top is closed and the longitudinal direction is set in thevertical direction. The reaction tube 2 is made of a heat-resistant andcorrosion-resistant material, such as quartz. In the reaction tube 2, aprocess field 2 a is defined to accommodate and process a plurality ofsemiconductor wafers (target substrates) stacked at intervals in thevertical direction.

On one side of the reaction tube 2, a long narrow exhaust port 3 b forvacuum-exhausting the inner atmosphere is formed by cutting the sidewallof the reaction tube 2 in, e.g., the vertical direction. The exhaustport 3 b is covered with an exhaust cover member 3 a, which is made ofquartz with a U-shape cross-section and attached by welding. The exhaustcover member 3 a extends upward along the sidewall of the reaction tube2, and has a gas outlet 4 at the top of the reaction tube 2. The gasoutlet 4 is connected to an exhaust section GE through an airtightexhaust line. The exhaust section GE has a pressure adjusting mechanismincluding, e.g., a valve and a vacuum exhaust pump (not shown in FIG. 1,but shown in FIG. 3 with a reference symbol 127). The exhaust section GEis used to exhaust the atmosphere within the reaction tube 2, and set itat a predetermined pressure (vacuum level).

A lid 5 is disposed below the reaction tube 2. The lid 5 is made of aheat-resistant and corrosion-resistant material, such as quartz. The lid5 is moved up and down by a boat elevator described later (not shown inFIG. 1, but shown in FIG. 3 with a reference symbol 128). When the lid 5is moved up by the boat elevator, the bottom of the reaction tube 2(load port) is closed. When the lid 5 is moved down by the boatelevator, the bottom of the reaction tube 2 (load port) is opened.

A wafer boat 6 made of, e.g., quartz is placed on the lid 5. The waferboat 6 is configured to hold a plurality of semiconductor wafers W atpredetermined intervals in the vertical direction. A thermallyinsulating cylinder may be disposed on the lid 5 to prevent thetemperature inside the reaction tube 2 from being lowered due to theload port of the reaction tube 2. Further, a rotary table may bedisposed to rotatably mount thereon the wafer boat 6 that holds thewafers W. In this case, the temperature of the wafers W placed on thewafer boat 6 can be more uniform.

The reaction tube 2 is surrounded by a temperature adjusting mechanism,such as a thermally insulating cover 71 and a heater 7, which is madeof, e.g., a resistive heating body and disposed on the inner surface ofthe cover 71. The process field 2 a inside the reaction tube 2 is heatedby the heater 7, so that the wafers W are heated up (increase intemperature) to a predetermined temperature.

Gas distribution nozzles 8 and 9 and a gas nozzle 16 penetrate thesidewall of the reaction tube 2 near the bottom, and are used forsupplying process gases (such as an oxidizing gas, a silicon source gas,and an inactive gas for dilution, purge, or pressure control) into thereaction tube 2. Each of the gas distribution nozzles 8 and 9 and gasnozzle 16 is connected to a process gas supply section GS through amass-flow controller (MFC) and so forth (not shown). The process gassupply section GS includes gas sources of the reactive gases and a gassource of nitrogen (N₂) gas used as an inactive gas, so as to prepare afirst process gas comprising a silicon source gas and a second processgas comprising an oxidizing gas, as described below.

Specifically, in this embodiment, in order to form a silicon oxide film(product film) on the wafers W by ALD or MLD, di-iso-propylaminosilane(DIPAS) gas is used as a silicon source gas in the first process gas andoxygen gas is used as an oxidizing gas in the second process gas. Eachof the first and second process gases may be mixed with a suitableamount of carrier gas (dilution gas, such as N₂ gas), as needed.However, such a carrier gas will be mentioned only when necessary,hereinafter, for the sake of simplicity of explanation.

The gas distribution nozzle 8 is connected to gas sources of O₂ gas andN₂ gas, the gas distribution nozzle 9 is connected to gas sources ofDIPAS gas and N₂ gas, and the gas nozzle 16 is connected to a gas sourceof N₂ gas. These gas sources are disposed in the process gas supplysection GS.

Each of the gas distribution nozzles 8 and 9 is formed of a quartz pipewhich penetrates the sidewall of the reaction tube 2 from the outsideand then turns and extends upward (see FIG. 1). Each of the gasdistribution nozzles 8 and 9 has a plurality of gas spouting holes, eachset of holes being formed at predetermined intervals in the longitudinaldirection (the vertical direction) over all the wafers W on the waferboat 6. Each set of the gas spouting holes delivers the correspondingprocess gas almost uniformly in the horizontal direction, so as to formgas flows parallel with the wafers W on the wafer boat 6. On the otherhand, the gas nozzle 16 used only for the inactive gas is formed of ashort gas nozzle, which penetrates the sidewall of the reaction tube 2from the outside.

A plasma generation section 10 is attached to the sidewall of thereaction tube 2 and extends in the vertical direction. The plasmageneration section 10 has a vertically long narrow opening 10 b formedby cutting a predetermined width of the sidewall of the reaction tube2′, in the vertical direction. The opening 10 b is covered with a quartzcover 10 a airtightly connected to the outer surface of the reactiontube 2 by welding. The cover 10 a has a vertically long narrow shapewith a concave cross-section, so that it projects outward from thereaction tube 2.

With this arrangement, the plasma generation section 10 is formed suchthat it projects outward from the sidewall of the reaction tube 2 and isopened on the other side to the interior of the reaction tube 2. Inother words, the inner space of the plasma generation section 10communicates with the process space within the reaction tube 2. Theopening 10 b has a vertical length sufficient to cover all the wafers Won the wafer boat 6 in the vertical direction.

A pair of long narrow electrodes 11 are disposed on the opposite outersurfaces of the cover 10 a, and face each other while extending in thelongitudinal direction (the vertical direction). The electrodes 11 areconnected to an RF (Radio Frequency) power supply 11 a for plasmageneration, through feed lines. An RF voltage of, e.g., 13.56 MHz isapplied to the electrodes 11 to form an RF electric field for excitingplasma between the electrodes 11. The frequency of the RF voltage is notlimited to 13.56 MHz, and it may be set at another frequency, e.g., 400kHz.

The gas distribution nozzle 8 of the second process gas is bent outwardin the radial direction of the reaction tube 2, at a position lower thanthe lowermost wafer W on the wafer boat 6. Then, the gas distributionnozzle 8 vertically extends at the deepest position (the farthestposition from the center of the reaction tube 2) in the plasmageneration section 10. As shown also in FIG. 2, the gas distributionnozzle 8 is separated outward from an area sandwiched between the pairof electrodes 11 (a position where the RF electric field is mostintense), i.e., a plasma generation area where the main plasma isactually generated. The second process gas comprising O₂ gas is spoutedfrom the gas spouting holes of the gas distribution nozzle 8 toward theplasma generation area. Then, the second process gas is excited(decomposed or activated) in the plasma generation area, and is suppliedin this state with radicals containing oxygen atoms (O* and O₂*) ontothe wafers W on the wafer boat 6 (the symbol ┌*┘ denotes that it is aradical).

At a position near and outside the opening 10 b of the plasma generationsection 10, the gas distribution nozzle 9 of the first process gas isdisposed. The gas distribution nozzle 9 extends vertically upward on oneside of the outside of the opening 10 b (inside the reaction tube 2).The first process gas comprising DIPAS gas is spouted from the gasspouting holes of the gas distribution nozzle 9 toward the center of thereaction tube 2. Accordingly, the first process gas supplied from thegas distribution nozzle 9 is not turned into plasma (or activated) bythe plasma generation section 10.

A plurality of temperature sensors 122, such as thermocouples, formeasuring the temperature inside the reaction tube 2 and a plurality ofpressure gages (not shown in FIG. 1, but shown in FIG. 3 with areference symbol 123) for measuring the pressure inside the reactiontube 2 are disposed inside the reaction tube 2.

The film formation apparatus 1 further includes a control section 100for controlling respective portions of the apparatus. FIG. 3 is a viewshowing the structure of the control section 100. As shown in FIG. 3,the control section 100 is connected to an operation panel 121, (a groupof) temperature sensors 122, (a group of) pressure gages 123, a heatercontroller 124, MFC controllers 125, valve controllers 126, a vacuumpump 127, a boat elevator 128, a plasma controller 129, and so forth.

The operation panel 121 includes a display screen and operation buttons,and is configured to transmit operator's instructions to the controlsection 100, and show various data transmitted from the control section100 on the display screen. The (group of) temperature sensors 122 areconfigured to measure the temperature at respective portions inside thereaction tube 2, exhaust line, and so forth, and to transmit measurementvalues to the control section 100. The (group of) pressure gages 123 areconfigured to measure the pressure at respective portions inside thereaction tube 2, exhaust line, and so forth, and to transmit measurementvalues to the control section 100.

The heater controller 124 is configured to control the heater 7. Theheater controller 124 turns on the heater to generate heat in accordancewith instructions from the control section 100. Further, the heatercontroller 124 measures the power consumption of the heater, andtransmits it to the control section 100.

The MFC controllers 125 are configured to respectively control the MFCs(not shown) connected to the gas distribution nozzles 8 and 9 and thegas nozzle 16. The MFC controllers 125 control the flow rates of gasesflowing through the MFCs in accordance with instructions from thecontrol section 100. Further, the MFC controllers 125 measure the flowrates of gases flowing through the MFCs, and transmit them to thecontrol section 100.

The valve controllers 126 are respectively disposed on piping lines andconfigured to control the opening rate of valves disposed on pipinglines in accordance with instructed values received from the controlsection 100. The vacuum pump 127 is connected to the exhaust line andconfigured to exhaust gas from inside the reaction tube 2.

The boat elevator 128 is configured to move up the lid 5, so as to loadthe wafer boat 6 (wafers W) into the reaction tube 2. The boat elevator128 is also configured to move the lid 5 down, so as to unload the waferboat 6 (wafers W) from the reaction tube 2.

The plasma controller 129 is configured to control the plasma generationsection 10 in accordance with instructions from the control section 100,so that oxygen gas supplied into the plasma generation section 10 isactivated to generate oxygen radicals.

The control section 100 includes a recipe storage portion 111, a ROM112, a RAM 113, an I/O port 114, and a CPU 115. These members areinter-connected via a bus 116 so that data can be transmitted betweenthem through the bus 116.

The recipe storage portion 111 stores a setup recipe and a plurality ofprocess recipes. After the film formation apparatus 1 is manufactured,only the setup recipe is initially stored. The setup recipe is executedwhen a thermal model or the like for a specific film formation apparatusis formed. The process recipes are prepared respectively for heatprocesses to be actually performed by a user. Each process recipeprescribes temperature changes at respective portions, pressure changesinside the reaction tube 2, start/stop timing for supply of processgases, and supply rates of process gases, from the time wafers W areloaded into the reaction tube 2 to the time the processed wafers W areunloaded.

The ROM 112 is a storage medium formed of an EEPROM, flash memory, orhard disc, and is used to store operation programs executed by the CPU115 or the like. The RAM 113 is used as a work area for the CPU 115.

The I/O port 114 is connected to the operation panel 121, temperaturesensors 122, pressure gages 123, heater controller 124, MFC controllers125, valve controllers 126, vacuum pump 127, boat elevator 128, andplasma controller 129, and is configured to control output/input of dataor signals.

The CPU (Central Processing Unit) 115 is the hub of the control section100. The CPU 115 is configured to run control programs stored in the ROM112, and control an operation of the film formation apparatus 1, inaccordance with a recipe (process recipe) stored in the recipe storageportion 111, following instructions from the operation panel 121.Specifically, the CPU 115 causes the (group of) temperature sensors 122,(group of) pressure gages 123, and MFC controllers 125 to measuretemperatures, pressures, and flow rates at respective portions insidethe reaction tube 2, exhaust line, and so forth. Further, the CPU 115outputs control signals, based on measurement data, to the heatercontroller 124, MFC controllers 125, valve controllers 126, and vacuumpump 127, to control the respective portions mentioned above inaccordance with a process recipe.

Next, an explanation will be given of a film formation method (so calledALD or MLD film formation) performed under the control of the controlsection 100 in the apparatus shown in FIG. 1. In this film formationmethod, a silicon oxide film is formed on semiconductor (Si) wafers W byplasma CVD. In order to achieve this, a first process gas comprisingDIPAS gas as a silicon source gas, and a second process gas comprisingoxygen (O₂) gas as an oxidizing gas are selectively supplied to theprocess field 2 a accommodating wafers W. FIG. 4 is a timing chartshowing the recipe of a film formation process according to theembodiment of the present invention.

The respective components of the film formation apparatus 1 describedbelow are operated under the control of the control section 100 (CPU115). The temperature and pressure of the process field 2 a and the gasflow rates during the processes are set in accordance with the recipeshown in FIG. 4, while the control section 100 (CPU 115) controls theheater controller 124 (for the heater 7), MFC controllers 125 (for thegas distribution nozzles 8 and 9 and gas nozzle 16), valve controllers126, vacuum pump 127, and plasma controller 129 (plasma generationsection 10), as described above.

At first, the wafer boat 6 at room temperature, which supports a numberof, e.g., 50 to 100, wafers having a diameter of 300 mm, is loaded tothe process field inside the reaction tube 2 set at a predeterminedtemperature, and the reaction tube 2 is airtightly closed. Then, theinterior of the reaction tube 2 is vacuum-exhausted and kept at apredetermined process pressure. Then, while the wafer boat 6 is rotated,the first and second process gases are intermittently supplied from therespective gas distribution nozzles 9 and 8 at controlled flow rates.

In summary, at first, the first process gas comprising DIPAS gas issupplied from the gas spouting holes of the gas distribution nozzle 9 toform gas flows parallel with the wafers W on the wafer boat 6. Whilebeing supplied, molecules of the DIPAS gas and molecules and atoms ofdecomposition products generated by gas decomposition are adsorbed onthe surface of the wafers W to form an adsorption layer (adsorptionstage).

Then, the second process gas comprising O₂ gas is supplied from the gasspouting holes of the gas distribution nozzle 8 to form gas flowsparallel with the wafers W on the wafer boat 6. The second process gasis selectively excited and partly turned into plasma when it passesthrough the plasma generation area between the pair of electrodes 11. Atthis time, oxygen radicals (activated species), such as O* and O₂*, areproduced. The radicals flow out from the opening 10 b of the plasmageneration section 10 toward the center of the reaction tube 2, and aresupplied into gaps between the wafers W in a laminar flow state. Whenoxygen radicals are supplied onto the wafers W, they react with Si inthe adsorption layer on the wafers W, and a thin film of silicon oxideis thereby formed on the wafers W (oxidation stage).

As shown in FIG. 4, the film formation method according to thisembodiment is arranged to alternately repeat first to fourth steps T1 toT4 so as to alternately repeat the adsorption and oxidation stages. Acycle comprising the first to fourth steps T1 to T4 is repeated a numberof times, such as 100 times, and thin films of silicon oxide formed byrespective times are laminated, thereby arriving at a silicon oxide filmhaving a target thickness.

Specifically, the first step T1 is arranged to perform supply of DIPAgas to the process field 2 a, while maintaining a shut-off state ofsupply of O₂ gas to the process field 2 a. The second step T2 isarranged to maintain the shut-off state of supply of the DIPA gas and O₂gas to the process field 2 a. The third step T3 is arranged to performsupply of the O₂ gas to the process field 2 a, while maintaining theshut-off state of supply of the DIPA gas to the process field 2 a.Further, through the third step T3, the RF power supply 11 a is set inan ON state to turn the O₂ gas into plasma by the plasma generationsection 10, so as to supply the O₂ gas in an activated state to theprocess field 2 a. The fourth step T4 is arranged to maintain theshut-off state of supply of the DIPA gas and O₂ gas to the process field2 a. N₂ gas used as a dilution or purge gas is kept supplied over thefirst to fourth steps T1 to T4.

Each of the second and fourth steps T2 and T4 is used as a purge step toremove the residual gas within the reaction tube 2. The term “purge”means removal of the residual gas within the reaction tube 2 byvacuum-exhausting the interior of the reaction tube 2 while supplying aninactive gas, such as N₂ gas, into the reaction tube 2, or byvacuum-exhausting the interior of the reaction tube 2 while maintainingthe shut-off state of supply of all the gases. In this respect, thesecond and fourth steps T2 and T4 may be arranged such that the firsthalf utilizes only vacuum-exhaust and the second half utilizes bothvacuum-exhaust and inactive gas supply. Further, the first and thirdsteps T1 and T3 may be arranged to stop vacuum-exhausting the reactiontube 2 while supplying each of the first and second process gases.However, where supplying each of the first and second process gases isperformed along with vacuum-exhausting the reaction tube 2, the interiorof the reaction tube 2 can be continuously vacuum-exhausted over theentirety of the first to fourth steps T1 to T4.

It should be noted that, in light of the film formation sequence, thetemperature of the process field 2 a is preferably set to be constantduring the film formation. Accordingly, in this embodiment, thetemperature of the process field 2 a is preferably set at the sametemperature, such as room temperature (e.g., 25°C.), over the adsorptionand oxidation stages. Further, the process field 2 a is preferably keptexhausted over the adsorption and oxidation stages.

More specifically, in the adsorption stage, at first, while nitrogen gasis supplied to the process field 2 a at a predetermined flow rate, asshown in FIG. 4, (c), the process field 2 a is set at a predeterminedtemperature, such as room temperature (e.g., 25°C.), as shown in FIG. 4,(a). In this case, since the process field 2 a is set at roomtemperature, the heater 7 is not used to heat the process field 2 a.Further, the reaction tube 2 is exhausted to set the process field 2 aat a predetermined pressure, such as 66.5 Pa (0.5 Torr), as shown inFIG. 4, (b). Then, DIPAS gas is supplied to the process field 2 a at apredetermined flow rate, such as 0.3 slm, as shown in FIG. 4, (d), andnitrogen gas is also supplied to the process field 2 a at apredetermined flow rate, as shown in FIG. 4, (c) (T1: flow step).

After the flow step of the adsorption stage is performed for 1 to 3seconds, such as 2 seconds, as shown in FIG. 4, (h), the supply of DIPASgas is stopped. On the other hand, nitrogen gas is kept supplied fromthe gas distribution nozzle 9 to the process field 2 a at apredetermined flow rate, as shown in FIG. 4, (c). Further, the reactiontube 2 is exhausted to exhaust gas from the process field 2 a (T2: purgestep).

In the oxidation stage subsequently performed, at first, while nitrogengas is supplied to the process field 2 a at a predetermined flow rate,as shown in FIG. 4, (c), the process field 2 a is set at a predeterminedtemperature, such as room temperature (e.g., 25° C.), as shown in FIG.4, (a). At this time, the reaction tube 2 is exhausted to set theprocess field 2 a at a predetermined pressure, such as 66.5 Pa (0.5Torr), as shown in FIG. 4, (b). Then, an RF power of 500 W is appliedbetween the electrodes 11 (RF: ON), as shown in FIG. 4, (g). Further,oxygen gas is supplied to a position between the electrodes 11 (insidethe plasma generation section 10) at a predetermined flow rate, such as1 slm, as shown in FIG. 4, (e). The oxygen gas thus supplied is excited(activated) into plasma between the electrodes 11 and generates radicalscontaining oxygen atoms (O* and O₂*). The radicals containing oxygenatoms thus generated are supplied from the plasma generation section 10to the process field 2 a. Further, nitrogen gas is also supplied fromthe gas distribution nozzle 9 to the process field 2 a at apredetermined flow rate, as shown in FIG. 4, (c) (T3: flow step).

The radicals flow out from the opening 10 b of the plasma generationsection 10 toward the center of the reaction tube 2, and are suppliedinto gaps between the wafers W in a laminar flow state. When radicalscontaining oxygen atoms are supplied onto the wafers W, they react withSi in the adsorption layer on the wafers W, and a thin film of siliconoxide is thereby formed on the wafers W.

After the flow step of the oxidation stage is performed for 5 to 30seconds, such as 8 seconds, as shown in FIG. 4, (h), the supply ofoxygen gas is stopped and the application of RF power is stopped. On theother hand, nitrogen gas is kept supplied from the gas distributionnozzle 9 to the process field 2 a at a predetermined flow rate, as shownin FIG. 4, (c). Further, the reaction tube 2 is exhausted to exhaust gasfrom the process field 2 a (T4: purge step).

As described above, a cycle alternately comprising the adsorption andoxidation stages in this orders is repeated a predetermined number oftimes. In each cycle, DIPAS is supplied onto the wafers W to form anadsorption layer, and then radicals containing oxygen atoms are suppliedto oxidize the adsorption layer, so as to form a silicon oxide film. Asa result, a silicon oxide film of high quality can be formed with highefficiency.

When the silicon oxide film formed on the surface of the semiconductorwafers W reaches a predetermined thickness, the wafers W are unloaded.Specifically, nitrogen gas is supplied into the reaction tube 2 at apredetermined flow rate, so that the pressure inside the reaction tube 2is returned to atmospheric pressure. Then, the lid 18 is moved down bythe boat elevator 25, and the wafer boat 6 is thereby unloaded out ofthe reaction tube 2, along with the wafers W.

FIGS. 7A to 7F are views schematically showing a reaction on the surfaceof a Si wafer where DIPAS gas is used as a silicon source gas.

The DIPAS gas supplied to the process field 2 a is heated and activatedinside the process field 2 a, and an adsorption layer containing siliconis formed on the surface of each semiconductor wafer W, as shown fromFIG. 7A to FIG. 7B. In FIG. 7A, an OH group present on the surface ofthe Si wafer W is derived from, e.g., the surface of an SiO₂ filmdeposited thereon in advance. The adsorption layer is formed to containno nitrogen (N), because N(CH(CH₃)₂)₂ is separated from silicon when theadsorption layer is formed. This N(CH(CH₃)₂)₂ is removed by the purgestep.

Then, after the purge step, oxygen radicals are supplied to the processfield 2 a. Consequently, as shown from FIG. 7C to FIG. 7D, theadsorption layer on the wafer W is oxidized (H in the adsorption layeris replaced with O), whereby a silicon oxide film is formed on the waferW. A cycle comprising the adsorption and oxidation described above isrepeated a number of times, whereby silicon oxide films are laminated,as shown from FIG. 7E to FIG. 7F.

As described above, DIPAS used as a silicon source gas is a univalentaminosilane and makes nitrogen hardly contained in a silicon oxide filmto be formed, whereby a silicon oxide film of high quality is obtained.Further, in this case, structural impediments, which impede moleculeadsorption, can hardly occur when the adsorption layer is formed, andthe adsorption rate is not decreased, whereby a high film formation rateis maintained. Further, DIPAS is thermally stable and facilitates itsflow rate control such that conventional systems can be used for thesource supply, resulting in high versatility.

During the film formation process, the temperature of the process field2 a is set to be −32° C. to 700° C. If the temperature of the processfield 2 a is lower than −32° C., supply of DIPAS used as a siliconsource gas may be hindered. This is so, because, in consideration of apressure loss caused by the process gas supply line, MFC, and so forthconnected to the DIPAS gas source, the lower limit temperature forproviding a practicable vapor pressure of DIPAS is −32° C. On the otherhand, if the temperature of the process field 2 a is higher than 700°C., the film quality and uniformity of film thickness of the formedsilicon oxide film may be deteriorated.

This temperature is preferably set to be within a range of roomtemperature to 500° C., more preferably of room temperature to 400° C.,and furthermore preferably of room temperature to 300° C. Such rangemakes it possible to well utilize the feature (effect) of forming a thinfilm at a lower temperature than ever before.

The flow rate of the DIPAS gas is preferably set to be 10 sccm to 10slm. If the flow rate is lower than 10 sccm, the DIPAS supply onto thesurface of the wafers W may become insufficient. If the flow rate ishigher than 10 slm, the DIPAS ratio contributory to adsorption onto thesurface of the wafers W may become too low. The flow rate of DIPAS gasis more preferably set to be 0.05 slm to 3 slm. This flow rate rangemakes it possible to promote the DIPAS reaction on the surface of thewafers W.

The pressure of the process field 2 a (process pressure) in the DIPASsupply is preferably set to be 0.133 Pa (1 mTorr) to 13.3 kPa (100Torr). This pressure range makes it possible to promote the DIPASreaction on the surface of the wafers W.

The flow rate of the oxygen gas is preferably set to be 0.1 sccm to 10slm. This flow rate range makes it possible to generate plasma withoutdifficulty and to supply oxygen radicals sufficient to form a siliconoxide film. The flow rate of oxygen gas is more preferably set to be 0.5slm to 5 slm. This pressure range makes it possible to stably generateplasma.

The RF power is preferably set to be 10 to 1,500 W. If the power islower than 10 W, it is difficult to generate oxygen radicals. If thepower is higher than 1,500 W, the quartz wall of the plasma generationsection 10 may be damaged. The RF power is more preferably set to be 50to 500 W. This power range makes it possible to efficiently generateradicals.

The pressure of the process field 2 a (process pressure) in the oxygensupply is preferably set to be 0.133 Pa (1 mTorr) to 13.3 kPa (100Torr). This pressure range makes it possible to easily generate oxygenradicals and to increase the mean free path of oxygen radicals in theprocess field 2 a. This pressure is more preferably set to be 40 Pa (0.3Torr) to 400 Pa (3 Torr). This pressure range makes it possible toeasily control the pressure of the process field 2 a.

The pressure inside the plasma generation section 10 (the pressure atthe gas spouting holes) is preferably set to be 0.133 Pa (1 mTorr) to13.3 kPa (100 Torr), and more preferably to be 70 Pa (0.53 Torr) to 400Pa (3 Torr). This pressure range makes it possible to generate plasmawithout difficulty and to supply oxygen radicals sufficient to form asilicon oxide film.

<Experiment 1>

In order to find a preferable temperature of the process field 2 a, asilicon oxide film was formed on semiconductor wafers W while the settemperature of the process field 2 a was adjusted to different values.At this time, the cycle rate and inter-substrate uniformity of the filmthickness were measured. The set temperature of the process field 2 awas adjusted to room temperature (25° C.), 75° C., 100° C., 200° C., and300° C.

FIG. 5 is a graph showing the relationship of the cycle rate of a filmthickness relative to the set temperature of a process field. FIG. 6 isa graph showing the relationship of the inter-substrate uniformity (±%)of a film thickness relative to the set temperature of a process field.The cycle rate shown in FIG. 5 is a ratio in the film thickness obtainedby one cycle (Å/cycle) at each set temperature of the process fieldrelative to that obtained at 25° C. used as the set temperature (i.e.,the film thickness obtained by one cycle at 25° C. was used as thereference value “1”).

As shown in FIG. 6, where the set temperature of the process field wasadjusted to a temperature within a range of room temperature (25° C.) to200° C., the inter-substrate uniformity was remarkably improved.Specifically, where the set temperature was within this temperaturerange, the inter-substrate uniformity thereby obtained was ½ to ⅕ of theinter-substrate uniformity obtained where the set temperature of theprocess field was 300° C. Further, as shown in FIG. 5, where the settemperature of the process field was adjusted to a temperature within arange of room temperature (25° C.) to 200° C., the cycle rate wasimproved. Specifically, where the set temperature was within thistemperature range, the cycle rate thereby obtained was 1.1 to 1.3 timesthe cycle rate obtained where the set temperature of the process fieldwas 300° C. Accordingly, it has been found that the temperature of theprocess field is most preferably set to be within a range of roomtemperature to 200° C.

<Experiment 2>

A silicon oxide film was formed by the method according to theembodiment described above and was observed by an X-ray photoelectronspectrometer (XPS) to examine its composition. As a result, it wasconfirmed that the silicon oxide film contained no nitrogen. Further, asilicon oxide film was formed by this method and was observed by anatomic force microscope (AFM) to perform image analysis of its surfaceroughness. As a result, it was confirmed that the silicon oxide film hada good surface morphology. Accordingly, it has been found that a siliconoxide film of high quality can be formed at a lower temperature, such asroom temperature, by the method described above.

<Experiment 3>

A silicon oxide film was formed by the method according to theembodiment described above and the film formation rate (deposition rate)per minute was measured and resulted in 1.5 nm/min. Further, it wasconfirmed that the adsorption rate was maintained and thus theproductivity was not lowered even under room temperature. This was so,probably because DIPAS used as a silicon source gas hardly causedstructural impediments and so adsorption of other molecules was lesshindered, in the process of Si adsorption in the adsorption stage.

<Experiment 4>

A silicon oxide film was formed under room temperature by use of each ofbivalent and trivalent aminosilane gases, such asBTBAS(SiH2(NHC(CH₃)₃)₂) and 3DMAS(SiH(N(CH₃)₂)₃), as a silicon sourcegas and the quality of the film thus formed was examined. As a result, asilicon oxide film of high quality was not formed under roomtemperature.

<Experiment 5>

A silicon oxide film was formed under room temperature by use ofSiH₃(N(CH₃)₂), which was a univalent aminosilane, as a silicon sourcegas and the process of the film formation was examined. As a result, theSiH₃(N(CH₃)₂) was thermally unstable and was difficult to control itsflow rate. Accordingly, it has been found that use of SiH₃(N(CH₃)₂) as asilicon source gas is undesirable in batch type processing apparatusesof the kind shown in FIG. 1 and that DIPAS, which is thermally stableand facilitates its flow rate control, is preferably usable for the samepurpose.

<Consequence and Modification>

As described above, according to the embodiment, a silicon oxide film isformed on semiconductor wafers W by repeating a plurality of times acycle comprising an adsorption stage for adsorbing Si by use of DIPASand an oxidation stage for oxidizing the adsorbed Si. Consequently, asilicon oxide film of high quality can be formed at a low temperature.

Since DIPAS is used as a silicon source gas, the adsorption rate is notdecreased, whereby the productivity is maintained. Further, DIPAS isthermally stable and facilitates its flow rate control such thatconventional systems can be used for the source supply, resulting inhigh versatility.

In the embodiment described above, the oxidizing gas is exemplified byoxygen. In this respect, another gas, such as ozone (O₃) or water vapor(H₂O), may be used to oxidize adsorbed Si on semiconductor wafers W. Forexample, where ozone is used as an oxidizing gas, process conditions arepreferably arranged such that the temperature of the process field 2 ais set to be −32° C. to 600° C., the pressure thereof is set at 655 Pa(5 Torr), and the flow rates of oxygen (O₂) and ozone are respectivelyset at 10 slm and about 250 g/Nm³.

In the embodiment described above, the temperature of the process field2 a is set at the same temperature (room temperature) over theadsorption stage and oxidation stage. In this respect, the temperatureof the process field 2 a may be set at different temperatures betweenthe adsorption stage and the oxidation stage. For example, thetemperature of the process field 2 a may be set at room temperature inthe adsorption stage and set at 100° C. in the oxidation stage.

In the embodiment described above, oxygen radicals are generated by useof plasma. In this respect, another medium, such as catalyst, UV, heat,or magnetic force, may be used to activate the oxidizing gas. Forexample, ozone may be supplied from an ozone generator into the reactiontube 2, while being activated by heat inside the reaction tube 2 or heatapplied inside a heating vessel outside the reaction tube 2.

In the embodiment described above, a silicon oxide film is formed onsemiconductor wafers W by repeating 100 times the cycle described above.Alternatively, for example, the repetition times of the cycle may be setto be smaller, such as 50, or set to be larger, such as 200. In suchcase, the flow rates of DIPAS and oxygen gases, the RF power, and soforth are adjusted in accordance with the repetition times of the cycleto provide the silicon oxide film with a predetermined thickness.

In the embodiment described above, a silicon oxide film is formed onsemiconductor wafers W. Alternatively, the present invention may beapplied to a case where another silicon-containing insulating film, suchas a silicon nitride film, is formed. In this case, for example, asilicon nitride film is formed on semiconductor wafers W by repeating aplurality of times a cycle comprising an adsorption stage for adsorbingSi by use of DIPAS and a nitridation stage for nitriding the adsorbed Siby use of a nitriding gas. The nitriding gas may be one or more gasesselected from the group consisting of ammonia (NH₃), nitrogen dioxide(N₂O), nitrogen oxide (NO), and nitrogen (N₂).

In the embodiment described above, nitrogen gas may be supplied as adilution gas when a process gas is supplied. In this respect, nonitrogen gas may be supplied when the process gas is supplied. However,the process gas preferably contains nitrogen gas as a dilution gas,because the process time can be more easily controlled if it is soarranged. The dilution gas consists preferably of an inactive gas, suchas nitrogen gas or another inactive gas, e.g., helium (He), neon (Ne),argon (Ar), krypton (Kr), or xenon (Xe) in place of nitrogen gas.

In the embodiment described above, a silicon source gas and nitrogen gasare supplied through a common gas supply nozzle. Alternatively, gassupply nozzles may be respectively disposed in accordance with the typesof gases. Further, a plurality of gas supply nozzles may be connected tothe sidewall of the reaction tube 2 near the bottom, to supply each gasthrough a plurality of nozzles. In this case, a process gas is suppliedthrough a plurality of gas supply nozzles into the reaction tube 2, andthereby more uniformly spreads in the reaction tube 2.

In the embodiment described above, the film formation apparatus employedis a heat processing apparatus of the batch type having a single-tubestructure. However, for example, the present invention may be applied toa vertical heat processing apparatus of the batch type having a processcontainer of the double-tube type, which is formed of inner and outertubes. Alternatively, the present invention may be applied to a heatprocessing apparatus of the single-substrate type. The target substrateis not limited to a semiconductor wafer W, and it may be a glasssubstrate for, e.g., an LCD.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1-20. (canceled)
 21. A film formation method for a semiconductor processfor forming a silicon-containing insulating film by CVD on a targetsubstrate, the method comprising: supplying diisopropylaminosilane(DIPAS) gas as a silicon source gas onto the target substrate; andsupplying a reactive gas onto the target substrate, the reactive gasbeing an oxidizing gas containing oxygen or a nitriding gas containingnitrogen, wherein the target substrate is subjected to a processtemperature set at room temperature through the film formation method,and said supplying a reactive gas is performed by supplying the reactivegas onto the target substrate while exciting the reactive gas by turningthe reactive gas into plasma in an exciting mechanism, therebygenerating radicals from the reactive gas and using the radicals tooxidize or nitride substances derived from the DIPAS gas, so as to formthe silicon-containing insulating film.
 22. The method according toclaim 21, wherein the target substrate is subjected to a processpressure set at a pressure of 0.133 Pa to 13.3 kPa in each of saidsupplying DIPAS gas and said supplying a reactive gas.
 23. The methodaccording to claim 21, wherein the exciting mechanism includes a plasmageneration section attached to a reaction chamber that accommodates thetarget substrate, and the reactive gas is supplied through the plasmageneration section onto the target substrate.
 24. The method accordingto claim 21, wherein said supplying DIPAS gas and said supplying areactive gas are alternately repeated a plurality of times.
 25. Themethod according to claim 21, wherein said supplying DIPAS gas and saidsupplying a reactive gas are alternately repeated a plurality of timeswith purging interposed therebetween of exhausting and removing residualgases on the target substrate without supplying either of the DIPAS gasand the reactive gas onto the target substrate.
 26. The method accordingto claim 21, wherein the reactive gas is the oxidizing gas, which isselected from the group consisting of oxygen gas, ozone gas, and watervapor gas.
 27. The method according to claim 21, wherein the reactivegas is the nitriding gas, which is ammonia gas.
 28. A film formationmethod for a semiconductor process for forming a silicon oxide film byCVD on a target substrate, the method comprising: supplyingdiisopropylaminosilane (DIPAS) gas as a silicon source gas onto thetarget substrate; and supplying an oxidizing gas onto the targetsubstrate, the oxidizing gas being selected from the group consisting ofoxygen gas, ozone gas, and water vapor gas, wherein the target substrateis subjected to a process temperature set at room temperature throughthe film formation method, and said supplying an oxidizing gas isperformed by supplying the oxidizing gas onto the target substrate whileexciting the oxidizing gas by turning the oxidizing gas into plasma inan exciting mechanism, thereby generating radicals from the oxidizinggas and using the radicals to oxidize substances derived from the DIPASgas, so as to form the silicon oxide film.
 29. The method according toclaim 28, wherein the target substrate is subjected to a processpressure set at a pressure of 0.133 Pa to 13.3 kPa in each of saidsupplying DIPAS gas and said supplying an oxidizing gas.
 30. The methodaccording to claim 28, wherein the exciting mechanism includes a plasmageneration section attached to a reaction chamber that accommodates thetarget substrate, and the oxidizing gas is supplied through the plasmageneration section onto the target substrate.
 31. The method accordingto claim 28, wherein said supplying DIPAS gas and said supplying anoxidizing gas are alternately repeated a plurality of times.
 32. Themethod according to claim 28, wherein said supplying DIPAS gas and saidsupplying an oxidizing gas are alternately repeated a plurality of timeswith purging interposed therebetween of exhausting and removing residualgases on the target substrate without supplying either of the DIPAS gasand the oxidizing gas onto the target substrate.
 33. The methodaccording to claim 28, wherein the oxidizing gas is oxygen gas.